The overall aim of this research is to develop a micro-amperometric, minimally invasive, self-compensating, biosensor to continuously monitor blood lactate levels of patients during off pump coronary bypase surgery, and in CCU, ICU, emergency rooms, or post operative rooms, in point of care applications. One of the primary limitations in many current Continuous Monitoring System biosensors is their susceptibility to biofouling and encapsulation, which causes interference, drift and inaccuracies in reported results. The proposed lactate biosensor consists of a small diameter precious metal wire with a thin film of lactate oxidase immobilized on its surface, and a diffusion limiting, biocompatible membrane overcoat. This sensor will have a rapid and linear response over a wide dynamic range, be stable, readily replaced by an attending aide, and will have a low cost disposable sensor element integrated with reuseable sending and data logging units. Under Phase I the sensor configuration will be optimized and a linear response at concentrations up to 20 mM in buffer solution and serum, stability for at least 24 hours, sensor output repeatability, and the ability to inherently compensate for the effects of biofouling and encapsulation will be demonstrated. The major innovations present in this proposed development include the self-compensation feature; the use of a multi-layer membrane structure to reduce interference; and the use of biocompatible diffusion limiting coatings to minimize biofouling and sensor encapsulation. Preliminary testing conducted under internal funding has shown preliminary sensor feasibility in buffer solution. Once the sensor configuration has been optimized and met the Phase I demonstration criteria, more detailed Phase II testing are planned.